<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" href="../bootstrap-5.1.3-dist/css/bootstrap.css">
    <script src="../bootstrap-5.1.3-dist/js/bootstrap.js"></script>
</head>
<style>
    div {
        width: 100px;
        height: 100px;
        float: left;
        margin: 15px;
        padding-top: 20px;
    }
</style>

<body class="container">
    <h3 align="center">圆角边框</h3>
    <div class="border border-primary rounded">rounded</div>
    <div class="border border-primary rounded-0">rounded-0</div>
    <div class="border border-primary rounded-top">rounded-top</div>
    <div class="border border-primary rounded-end">rounded-end</div>
    <div class="border border-primary rounded-bottom">rounded-bottom</div>
    <div class="border border-primary rounded-start">rounded-start</div>
    <div class="border border-primary rounded-circle">rounded-circle</div>
    <div class="border border-primary rounded-pill">rounded-pill</div>
</body>

</html>